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From: Christoph Hellwig <hch@lst.de>
To: Baoquan He <bhe@redhat.com>
Cc: Christoph Lameter <cl@gentwo.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	akpm@linux-foundation.org, hch@lst.de, robin.murphy@arm.com,
	penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com,
	vbabka@suse.cz, m.szyprowski@samsung.com,
	John.p.donnelly@oracle.com, kexec@lists.infradead.org
Subject: Re: [PATCH RESEND v2 0/5] Avoid requesting page from DMA zone when no managed pages
Date: Mon, 13 Dec 2021 08:49:19 +0100	[thread overview]
Message-ID: <20211213074919.GC20758@lst.de> (raw)
In-Reply-To: <20211213073925.GA29905@MiWiFi-R3L-srv>

On Mon, Dec 13, 2021 at 03:39:25PM +0800, Baoquan He wrote:
> > > As said at above, ia64 and riscv don't have ZONE_DMA at all, they just
> > > cover low 4G with ZONE_DMA32 alone.
> > 
> > If you do not have devices that are crap and cannot address the full
> > memory then you dont need these special zones.
> 
> I am not a DMA expert, with my understanding, on x86_64 and arm64, we
> have PCIe devices which dma mask is 32bit

Yes, way to many, and they keep getting newly introduce as well.  Also
weirdo masks like 40, 44 or 48 bits.

> , means they can only address
> ZONE_DMA32.

Yes and no.  Offset between cpu physical and device address make this
complicated, even ignoring iommus.

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WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Baoquan He <bhe@redhat.com>
Cc: Christoph Lameter <cl@gentwo.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	akpm@linux-foundation.org, hch@lst.de, robin.murphy@arm.com,
	penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com,
	vbabka@suse.cz, m.szyprowski@samsung.com,
	John.p.donnelly@oracle.com, kexec@lists.infradead.org
Subject: Re: [PATCH RESEND v2 0/5] Avoid requesting page from DMA zone when no managed pages
Date: Mon, 13 Dec 2021 08:49:19 +0100	[thread overview]
Message-ID: <20211213074919.GC20758@lst.de> (raw)
In-Reply-To: <20211213073925.GA29905@MiWiFi-R3L-srv>

On Mon, Dec 13, 2021 at 03:39:25PM +0800, Baoquan He wrote:
> > > As said at above, ia64 and riscv don't have ZONE_DMA at all, they just
> > > cover low 4G with ZONE_DMA32 alone.
> > 
> > If you do not have devices that are crap and cannot address the full
> > memory then you dont need these special zones.
> 
> I am not a DMA expert, with my understanding, on x86_64 and arm64, we
> have PCIe devices which dma mask is 32bit

Yes, way to many, and they keep getting newly introduce as well.  Also
weirdo masks like 40, 44 or 48 bits.

> , means they can only address
> ZONE_DMA32.

Yes and no.  Offset between cpu physical and device address make this
complicated, even ignoring iommus.


  reply	other threads:[~2021-12-13  7:49 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-07  3:07 [PATCH RESEND v2 0/5] Avoid requesting page from DMA zone when no managed pages Baoquan He
2021-12-07  3:07 ` Baoquan He
2021-12-07  3:07 ` [PATCH RESEND v2 1/5] docs: kernel-parameters: Update to reflect the current default size of atomic pool Baoquan He
2021-12-07  3:07   ` Baoquan He
2021-12-07  3:53   ` John Donnelly
2021-12-07  3:53     ` John Donnelly
2021-12-07  3:07 ` [PATCH RESEND v2 2/5] dma-pool: allow user to disable " Baoquan He
2021-12-07  3:07   ` Baoquan He
2021-12-07  3:53   ` John Donnelly
2021-12-07  3:53     ` John Donnelly
2021-12-13  7:44   ` Christoph Hellwig
2021-12-13  7:44     ` Christoph Hellwig
2021-12-13  8:16     ` Baoquan He
2021-12-13  8:16       ` Baoquan He
2021-12-07  3:07 ` [PATCH RESEND v2 3/5] mm_zone: add function to check if managed dma zone exists Baoquan He
2021-12-07  3:07   ` Baoquan He
2021-12-07  3:53   ` John Donnelly
2021-12-07  3:53     ` John Donnelly
2021-12-07 11:23   ` David Hildenbrand
2021-12-07 11:23     ` David Hildenbrand
2021-12-09 13:02     ` Baoquan He
2021-12-09 13:02       ` Baoquan He
2021-12-09 13:10       ` David Hildenbrand
2021-12-09 13:10         ` David Hildenbrand
2021-12-09 13:23         ` Baoquan He
2021-12-09 13:23           ` Baoquan He
2021-12-07  3:07 ` [PATCH RESEND v2 4/5] dma/pool: create dma atomic pool only if dma zone has managed pages Baoquan He
2021-12-07  3:07   ` Baoquan He
2021-12-07  3:07   ` Baoquan He
2021-12-07  3:54   ` John Donnelly
2021-12-07  3:54     ` John Donnelly
2021-12-07  3:54     ` John Donnelly
2021-12-07  3:07 ` [PATCH RESEND v2 5/5] mm/slub: do not create dma-kmalloc if no managed pages in DMA zone Baoquan He
2021-12-07  3:07   ` Baoquan He
2021-12-07  3:54   ` John Donnelly
2021-12-07  3:54     ` John Donnelly
2021-12-07  3:16 ` [PATCH RESEND v2 0/5] Avoid requesting page from DMA zone when no managed pages Baoquan He
2021-12-07  3:16   ` Baoquan He
2021-12-07  4:03   ` John Donnelly
2021-12-07  4:03     ` John Donnelly
2021-12-08  4:33     ` Andrew Morton
2021-12-08  4:33       ` Andrew Morton
2021-12-08  4:56       ` John Donnelly
2021-12-08  4:56         ` John Donnelly
2021-12-13  3:54     ` Baoquan He
2021-12-13  3:54       ` Baoquan He
2021-12-13 13:25   ` Borislav Petkov
2021-12-13 13:25     ` Borislav Petkov
2021-12-13 14:03     ` Baoquan He
2021-12-13 14:03       ` Baoquan He
2021-12-07  8:05 ` Christoph Lameter
2021-12-07  8:05   ` Christoph Lameter
2021-12-09  8:05   ` Baoquan He
2021-12-09  8:05     ` Baoquan He
2021-12-09 12:59     ` Christoph Lameter
2021-12-09 12:59       ` Christoph Lameter
2021-12-13  7:39       ` Baoquan He
2021-12-13  7:39         ` Baoquan He
2021-12-13  7:49         ` Christoph Hellwig [this message]
2021-12-13  7:49           ` Christoph Hellwig
2021-12-13 14:21       ` Hyeonggon Yoo
2021-12-13 14:21         ` Hyeonggon Yoo
2021-12-13  7:47   ` Christoph Hellwig
2021-12-13  7:47     ` Christoph Hellwig

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